Putting the squeeze on atoms and molecules

When the pressure is on, strange and wonderful things happen in the world of the super-small.

Life can only exist in a narrow range of pressures and temperatures, and chemistry and physics is mainly focused around the study of these “normal”, life-permitting conditions. But recent advances in high-pressure chemistry and physics have made it possible to break open these limitations, reaching ultra-high pressures and temperatures in laboratories (up to 4 million times the atmospheric pressure and as high as 3700 degrees), giving access to materials with unusual structural, electronic and magnetic properties. Even more extreme conditions occur in detonations of high-energy materials, in the interior of planets, or in comet collisions.

Normal chemistry changes dramatically at high pressures: chemical bonds break and new ones form, hydrogen becomes metallic, nitrogen forms strands, and lithium liquifies. Distances between atoms decrease, and both electronic and structural modifications can lead to new and unexpected electronic properties.

High pressure may also have played an important role in the origins of life and in the synthesis of the first biologically relevant organic molecules such as amino acids. Discovery of abundant life in high-pressure environments such as the deep-ocean, hydrothermal vents or crustal rocks shows that life is able to adapt to such extreme and harsh conditions.

Development of new materials

Studies of atoms and molecules at high pressure stretches current chemical intuition and leads to the development of new materials with novel structural, electronic and magnetic properties. Materials’ chemistry under ultra-high pressure is an important emerging research area, opening up exciting new routes for stabilising unusual and interesting compounds. A clear theoretical framework is, however, needed in order to gain a deeper understanding, and predict new chemistry and physics while guiding the difficult experiments.

In a new project, funded by a Marsden grant, Distinguished Professor Peter Schwerdtfeger and Dr Elke Pahl from the Centre for Theoretical Chemistry and Physics at the New Zealand Institute for Advanced Study at Massey University, Albany, with support from postdoctoral fellows Dr Krista Steenbergen and Dr Paul Jerabek and PhD students Odile Smits and Lukas Trombach, are working to create just such a theoretical framework to gain a deeper understanding of high-pressure physics.

To do this, they are developing state-of-the-art computational methods in order to investigate high-pressure materials as accurately as can be achieved in experiments. Simulations are being carried out at Massey University’s high-performance computer cluster, coupled with the use of sophisticated quantum chemistry software packages.

Previously, the team has successfully simulated the liquid-to-gas transition of mercury, explaining for the first time why it has such a low boiling point compared to the lighter elements in the periodic table. Their results showed that due to Einstein’s special relativity, mercury becomes chemically more inert, lowering the transition temperature by 300 degrees.

Exotic element copernicum

Currently, they are gaining understanding of the element copernicum, an exotic, superheavy synthetic element that can only be created in a laboratory. It is radioactive and very short-lived (its half-life is seconds or minutes). Much about it is unknown, including whether it is a liquid or even a gas at room temperature. The team has begun simulating the melting of copernicum to answer this long-standing question.

The team has also succeeded in calculating solid-state properties of the rare gas element argon to an unprecedented accuracy, in perfect agreement with experimental results. Preliminary high-pressure simulations confirm experimental results for a phase transition at high pressures and provide detailed insight into the mechanism.

World-leading authority

Distinguished Professor Peter Schwerdtfeger
Overall, the research requires expertise in many important fields such as atomic, molecular and solid-state physics, statistical physics and thermodynamics, quantum chemistry, materials, computer science and mathematics. The team is in a good position to achieve this with Professor Schwerdtfeger at the helm. A world-leading authority in quantum chemistry and physics, he was the 2014 winner of the Royal Society of New Zealand’s Rutherford Medal. He has received many international grants, awards and prizes, including a James Cook Fellowship and the Hector Medal in 2001, the Alexander von Humboldt Research

Prize and the Fukui medal in 2011, and an elected fellowship into the International Academy of Quantum Molecular Sciences in 2012. He was made a Distinguished Professor in 2012.

In the future, the team aims to study methane encapsulation in ice under pressure, a system that is currently not well understood but is important in understanding methane emission from ice on ocean floors and in permafrost regions.

Encapsulated methane is considered a danger to our climate should melting cause an uncontrolled release. More generally, this part of the project will significantly enhance understanding of the stability and the melting behaviour of molecular compounds under pressure.

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Last updated on Friday 28 October 2016

"Simulations are being carried out at Massey University’s high-performance computer cluster, coupled with the use of sophisticated quantum chemistry software packages."